[receiver/httpcheck] fail fast on endpoint missing scheme (#23808)

Fixes #23020

.chloggen/httpcheck-parse-scheme.yaml

@@ -0,0 +1,24 @@
+# Use this changelog template to create an entry for release notes.
+# If your change doesn't affect end users, such as a test fix or a tooling change,
+# you should instead start your pull request title with [chore] or use the "Skip Changelog" label.
+
+# One of 'breaking', 'deprecation', 'new_component', 'enhancement', 'bug_fix'
+change_type: breaking
+
+# The name of the component, or a single word describing the area of concern, (e.g. filelogreceiver)
+component: receiver/httpcheck
+
+# A brief description of the change.  Surround your text with quotes ("") if it needs to start with a backtick (`).
+note: Fail fast on endpoint missing scheme
+
+# Mandatory: One or more tracking issues related to the change. You can use the PR number here if no issue exists.
+issues: [23020]
+
+# (Optional) One or more lines of additional information to render under the primary note.
+# These lines will be padded with 2 spaces and then inserted directly into the document.
+# Use pipe (|) for multiline entries.
+subtext: |
+  Previously, when configured with an endpoint without HTTP/HTTPS scheme like "opentelemetry.io",
+  the receiver would start correctly, but fail to check the endpoint, producing the `httpcheck.error`
+  metric on every collection interval. After this change, the receiver fails to start, writing
+  an error log saying that you need to provide a scheme in the endpoint.

receiver/httpcheckreceiver/config.go

@@ -18,7 +18,7 @@ import (
 // Predefined error responses for configuration validation failures
 var (
 	errMissingEndpoint = errors.New(`"endpoint" must be specified`)
-	errInvalidEndpoint = errors.New(`"endpoint" must be in the form of <scheme>://<hostname>:<port>`)
+	errInvalidEndpoint = errors.New(`"endpoint" must be in the form of <scheme>://<hostname>[:<port>]`)
 )
 
 // Config defines the configuration for the various elements of the receiver agent.
@@ -39,11 +39,11 @@ func (cfg *targetConfig) Validate() error {
 
 	if cfg.Endpoint == "" {
 		err = multierr.Append(err, errMissingEndpoint)
-	}
-	_, parseErr := url.Parse(cfg.Endpoint)
-	if parseErr != nil {
-		wrappedErr := fmt.Errorf("%s: %w", errInvalidEndpoint.Error(), parseErr)
-		err = multierr.Append(err, wrappedErr)
+	} else {
+		_, parseErr := url.ParseRequestURI(cfg.Endpoint)
+		if parseErr != nil {
+			err = multierr.Append(err, fmt.Errorf("%s: %w", errInvalidEndpoint.Error(), parseErr))
+		}
 	}
 
 	return err

receiver/httpcheckreceiver/config_test.go

@@ -66,6 +66,21 @@ func TestValidate(t *testing.T) {
 				fmt.Errorf("%w: %s", errInvalidEndpoint, `parse "invalid://endpoint:  12efg": invalid port ":  12efg" after host`),
 			),
 		},
+		{
+			desc: "missing scheme",
+			cfg: &Config{
+				Targets: []*targetConfig{
+					{
+						HTTPClientSettings: confighttp.HTTPClientSettings{
+							Endpoint: "www.opentelemetry.io/docs",
+						},
+					},
+				},
+			},
+			expectedErr: multierr.Combine(
+				fmt.Errorf("%w: %s", errInvalidEndpoint, `parse "www.opentelemetry.io/docs": invalid URI for request`),
+			),
+		},
 		{
 			desc: "valid config",
 			cfg: &Config{
@@ -75,6 +90,11 @@ func TestValidate(t *testing.T) {
 							Endpoint: "https://opentelemetry.io",
 						},
 					},
+					{
+						HTTPClientSettings: confighttp.HTTPClientSettings{
+							Endpoint: "https://opentelemetry.io:80/docs",
+						},
+					},
 				},
 			},
 			expectedErr: nil,